Various types of separation apparatus and methods have been used for the separation of fine solid particles from a medium in which they are dispersed. Particular reference can be made to simple sieve racks, hydrocyclones, and other types of apparatus making use of hydraulic separation. In both the coal and mineral industries, special techniques are employed to concentrate the assay value of an ore through processes based on either the specific-gravity or surface characteristics of the ore particles. However, essentially all processes used to concentrate the assay of an ore or coal have deteriorating performance as the particle size decreases. This results in the purity of the product decreasing with particle size. Various sizing apparatus have been used after the concentration process to sort similar quality particles by size with the objective of retrieving the desired quality particles as a product and sending the remaining sizes either to further processing or to discard, depending on their quality. Some specific gravity based beneficiation techniques employ a heavy media suspension, comprised of very fine sized magnetite or ferrosilicon (less than 0.04 mm diameter) and water, to separate lighter specific gravity ore or coal particles from heavier specific gravity particles. Preceding the introduction of the feed into the heavy-media suspension, a desliming step is typically used to remove fine size particles from the remaining coarser size feed fraction to insure the media does not become contaminated with fine, non-magnetic material. In addition, after the gravity separation step is complete, the media must be separated from the product and discard streams to insure an uncontaminated product and to also permit recovery and reuse of the magnetite.
In the above industrial practice, the sizing operation requires a device that can effectively remove finer than 0.044 mm diameter (separating size ranging from 0.21 mm to 0.044 mm) from the coarser size particles with the device separating these particles predominantly by physical size, exclusive of particle specific gravity. In general it may be said that all particle processing industries that concentrate a substance are in need of a simple apparatus and methods which will make it possible to produce a desired size product that will comply with quality specifications.